1. Field of the Invention
The present invention relates generally to the measurement of time varying analog signals and, more particularly, to a method and apparatus for obtaining and displaying a close approximation of the final stabilized value of the analog signal before the signal reaches stabilization. The invention is particularly well suited for use with electrochemical measuring devices, such as pH meters and the like, which generate a drifting analog signal and require that the signal stabilize before an accurate reading can be taken.
2. Description of the Prior Art
Measuring apparatus for taking analytical measurements typically employ a sensor for monitoring a parameter of interest and for generating an analog output signal which provides a measure of the parameter. The response time of the apparatus will depend upon the nature of the measured parameter, the particular analytical method employed, and the type of sensor. For example, in electrochemical analyzers having sensors for monitoring characteristics of chemical reactions, the reaction proceeds to completion over a period of time and the response time of the system is primarily determined by the reaction time itself. In other types of measurements, such as potentiometric measurements employing electrochemical probes for measuring solution pH and the like, the probe or sensor requires a finite time to stabilize after insertion into the solution and the response time of the system is determined primarily by the sensor response. In either case, the sensor will generate a time-varying analog output signal which drifts toward a stabilized final value.
Typically, the drifting output signal in the foregoing apparatus is displayed to an operator, and the operator observes the display and takes a reading when it appears that the displayed signal has stabilized at a final value. Thus, for an analog display indicator, such as a deflecting needle, the operator waits until the needle appears to have stopped moving. For digital displays, the operator waits until the displayed number has remained at the same value for some period. It is evident that if the operator misjudges and takes the reading too soon the recorded value will be in error. On the other hand, valuable time will be wasted if the operator waits an excessive length of time for stabilization.